As is known in the art, liquid crystal devices are used in wide range of applications, such as in displays, light valves, spatial light modulators, and optical phased arrays. One commonly used type of liquid crystal, nematics, have an elongated molecular structure, which results in an ordinary (no), and extraordinary (ne) refractive index along the short and long axis of the molecules, respectively. The arrangement of the molecules is not random as in liquids, but instead the molecules align to one another in a preferred direction defined as a so-called director. Due to molecular dipoles (permanent or induced), the director can be rotated by applying an electric (or magnetic) field.
Referring to FIG. 1, a typical nematic liquid crystal device, or cell, 10 includes a thin layer 12 of liquid crystal which is encapsulated between two flat substrates 14a, 14b, with here both substrates 14a, 14b having conducting films 16a, 16b, (electrodes) respectively, and at least one of the electrodes 16a, 16b being optically transparent. Electromagnetic radiation with a polarization angle parallel to the liquid crystal molecules plane of rotation represented by arrow 18 entering the liquid crystal cell 10 sees a varying refractive index as the director is rotated by applying an electric field passing through the layer 12 of liquid crystal because of a voltage applied to the electrodes 16a, 16b. Thus, the exiting radiation, indicated by the arrow 18′, will have a varying transit time through the cell, which is dependant upon the orientation of the liquid crystal director. In short, the cell imposes a tunable phase delay in accordance with the voltage between the electrodes 16a, 16b. This tunable phase delay can be utilized to construct devices such as phase retarders, special light modulators and optical phased arrays.
However, proper operation of the cell 10 requires that the liquid crystal's director relax to a known, repeatable, well-defined orientation in the absence of an applied field. The resting orientation of a liquid crystal's director is controlled in both azimuth and elevation by surface treatments or interfacial layers, sometimes referred to as director alignment layers, applied to the inner surfaces of the substrates 14a, 14b. These surface treatments/layers, or director alignment layers, shown in FIG. 1 as alignment layers 17 and can cause parallel (homogeneous) or perpendicular (homeotropic) alignment between the director and substrate. In the thin cell devices above, electric fields are applied across the gap between the substrates, causing the directors to rotate such as to be normal to the substrates. Therefore, in a resting state, the alignment layers should force the director into a homogeneous alignment to maximize the dynamic range of the device. To avoid the formation of disclinations (domain boundaries within the liquid crystal) alignment layers are designed to produce a slight elevation of the quiescent directors. This elevation angle, referred to as a tilt bias angle, is typically several degrees with respect to the substrate surface, and constrains the directors to a single rotational direction in response to the electric field.
The most common alignment technique is the use of a polymer film (typically a polyimide) which is rubbed by an organic fiber cloth. Alignment can routinely be obtained parallel to the rubbing direction with a tilt bias of several degrees. However, the use of polymer films, which are sensitive to mechanical, chemical, and thermal degradation, imposes significant processing limitation on device fabrication. Once the polymer films have been applied, the maximum processing temperature must remain low (<300 degrees C.), restricting the use of processes such as glass frit sealing and flip-chip solder bonding. In addition, the substrates cannot be solvent cleaned to remove contaminants prior to assembly. Finished devices are also restricted from use at elevated temperatures, such as high power laser, applications which can cause localized heating.
Obliquely deposited inorganic films, such as silicon monoxide SiO, have been developed which are an alternative to rubbed polymer alignment layer. Here the oblique angle between the SiO deposition flux and substrate normal is typically between 45 and 90 degrees. See Applied Physics Letters 21, 173 (1972), J. L. Janning. Early reports indicated modest control of the tilt bias (between 20 degrees and 30 degrees) by varying the angle between the substrate and SiO deposition flux (see Lett. Appl, Eng. Sci., 1, 19 (1973), E. Guyon, P. Pieranski and M. Boix) or by varying the SiO thickness (See Jpn J. Appl. Phy., 19, 5567 (1980) K. Hirosima and M. Mochizuki). The needs for lower tilt biases in higher performance devices have motivated further development of SiO alignment layers. Meyerhofer and Johnson et. al (Appl. Phys. Lett, 29, 691 (1967), IEEE Trans. Elect. Dev., ED-24, 805 (1977) demonstrated multi-layer SiO deposition techniques that yielded low lilt bias; however, the technique requires extremely thin (˜5 Angstrom) layers that are difficult to reproduce in large area/high volume production. Recently, Smith et. al (see U.S. Pat. No. 5,512,148) demonstrated that ion beam sputter deposited SiO treated with alcohol will produce low tilt bias alignment; however, the use of organic thin films imposes the same problems as rubbed polymer films.
One apparatus used to provide the SiO deposition is shown in FIG. 2. Here, the substrate 14b is supported in a vacuum chamber such that the substrate normal 18 is at an angle here 85 degrees to the direction of a deposition flux (i.e., the evaporated species used to deposit the SiOx director alignment layer 17, FIG. 1), as indicated. The effect of such process is to “grow” columns 17 of SiOx, as shown in FIG. 3. The directors are indicated by numerical designation 19 in FIG. 3. It is first noted that the columns 17 have a longitudinal axis 21 which is at an oblique angle, α, typically no smaller than 50 degrees with respect to the surface of the substrate 14b. 
Referring also to FIG. 4, it is noted that the effect of the impacting deposition flux of SiOx is to form the distal end 20 of the column 17 of SiOx, with a surface 22a, 22b, 22c that grows towards an oblique angle β (FIG. 3) with respect to the surface of the substrate 14b. It is first noted that the directors are substantially flat and aligned substantial parallel to the surface of the SiOx columns 17. It is next noted that the near director field (indicated by numerical designation 24a) is parallel to the directors 19. Thus, the near director field 24a is parallel to the longitudinal axis 21 of the column 17 in the region more proximate the surface of the substrate 14b; however, the far director field (indicated in FIG. 3 by numerical designation 24b) tends to deviate in angular direction towards surface 22 at the distal end of the column 17. Thus, the effective tilt angle of the cell is the angle γ. Typically, the effective director tilt angle γ is relatively high, e.g., in the order of 20 degrees, thereby reducing the dynamic range of the cell. It should be noted that the angle of the longitudinal axis 21 relative to the surface of the substrate, i.e, the angle α, is limited by the kinetics of the growing process used to form the columns and not by the angle between the deposition flux and the normal 18 to the surface of the substrate (FIG. 2)